1. Field of the Invention
This invention relates to a working mechanism having utility in a variety of applications and being operable to reliably move one or a plurality of elongated working elements at variable speeds along a virtual infinity of complex paths. The mechanism specifically can be adapted to successively separate interconnected sheets of a zigzag folded web and move the sheets for further processing such as collation or stitching.
2. Description of the Prior Art
Very few mechanical devices are known for providing variable speed motion along an irregular closed loop path, as opposed to the numerous devices available for producing reciprocable or rotatable movements. Generally, complex motions in machinery have conventionally been provided by employing various cam mechanisms having a camming surface in cooperative engagement with a cam follower. While such devices may be satisfactory for driving a single movable element connected to the cam follower, a variety of virtually insurmountable problems are encountered when more than one movable element is needed.
By way of example, a cam controlled Geneva wheel can produce a rotational movement having a variable speed. In this device, a driving disc carries a radially movable pin which has a longitudinal axis parallel to the rotational axis of the disc. As the disc rotates, the pin enters an internal fixed cam pathway which moves the pin in a radial direction relative to the disc. Additionally, an output wheel adjacent the disc has a radially oriented slot engageable with the pin when the latter travels along the cam pathway, whereby the rotational speed of the output wheel varies as the pin follows the configuration of the pathway. Obviously, such a device cannot be used to simultaneously provide dissimilar movement to a number of working elements connected to the output wheel. Additionally, the Geneva typically can move the working elements only in a rotational direction unless an additional, motion-translating device is used.
Other cam constructions have been proposed in the past to provide both non-circular movement and acceleration and deceleration along the path of travel. U.S. Pat. No. 3,777,927, for example, discloses a cam device comprising a number of Z-shaped working elements pivotally coupled at spaced intervals to a movable, endless roller chain. A cam on one leg of each of the elements selectively engages a stationary camming surface disposed at a certain location adjacent the chain, such that the element will supposedly pivot as the chain moves the element near the camming surface. A working portion on the element remote from the cam thus swings relative to chain movement in an attempt to fold the rear flaps of boxes traveling on an adjacent conveyor. Unfortunately, the swinging movement of the element cannot always be precisely controlled because the cam is not confined to a location adjacent the camming surface.
So-called internal cams have been proposed in the past in attempt to overcome the deficiencies of conventional cam devices, and to provide irregular motions for associated linkage arms or the like. However, use of the internal cams inherently presents numerous obstacles which cannot be easily overcome. For instance, very irregular cam pathways must be precisely machined to eliminate undesirable "slop" or "give" which could otherwise allow undesired movement of the cam. Such tolerances are particularly important whenever the cam mechanism is designed to provide a motion reversal of the associate linkage arm, inasmuch as the cam must move from a "leading" to a "lagging" position relative to the linkage arm. Additionally, other mechanisms may be required to ensure that the cam is either leading or lagging as the cam is moved away from the changeover position. Thus, use of such internal cam devices has been rather limited to mechanisms which provide a relatively slow movement along a somewhat simple path of travel.